At least one invention pertains to compositions and methods for reducing biological activity in process streams, e.g. water based process streams. Biological activity in process streams is problematic for a variety of reasons, including, but not limited to sanitation problems, process equipment efficiency problems, and product quality problems. For example, in papermaking processes, high biological activity levels have a deleterious effect on equipment operation. The problems associated with manufacturing certain paper types, e.g. tissue/recycled products, are more pronounced, because high fungal levels present the quandary of providing a biocide program that stabilizes the biocide well enough so that it is not readily consumed (good persistence) and providing a biocide at sufficient levels to combat periodic spikes in biological activity—a need for less stabilization/decreased persistence. Moreover, bleaching/processing of recycled fiber presents the additional quandary for papermakers because papermakers are balancing the addition of sulfite post bleaching/processing of recycled fibers, which quenches a halogen, e.g. chlorine, with the need to maintain chlorine in the system, more specifically, a persistent level of chlorine in the papermaking system without having to add more halogen/chlorine than is necessary. Thus, there is a need for a further refinement of biocide-stabilizer formulations and delivery protocols, which can treat systems more effectively and in an environmental friendly manner, such as using less chlorine/halogen, which in turn reduces halogen by-product formation.
At least one invention relates to methods and compositions effective at stabilizing oxidant biocides. Oxidant biocides such as peroxide acid and halogen chemicals like sodium hypochlorite have been widely used in the pulp and paper industry. These oxidant biocides are highly effective at immediately killing large numbers of microorganisms. Unfortunately, after their introduction into process water systems, oxidant biocides are not naturally stable and they tend to oxidize rapidly and over time lose their effectiveness. In environments with very high populations of microorganisms such as in process water which is rich in organic and inorganic material on which the microorganisms can feast, sufficient numbers of microorganisms can survive until after the oxidant biocides have lost effectiveness. As a result, unless there is sufficient residual biocide present, the microorganism population will soon recover from an oxidant biocide treatment. In some cases, halogen tolerant bacteria strains develop due to repeated introduction of single oxidant biocide. This can result in systems suffering from out of control bacterial growth. (See for example the textbook: Disinfection, Sterilization, and Preservation, Fifth Edition, by Seymour S. Block, Lippincott Williams & Wilkins, (2001) at least in pp. 31-57).
This problem is compounded by the fact that repeated applications of oxidant biocides is in many contexts, not commercially feasible. Many oxidant biocides cause adverse effects on paper brighteners, dyes, and other additives required to produce commercially acceptable paper products. Repeated introduction of oxidant biocides can also corrode many pieces of papermaking machinery.
One technique used to address this problem is to stabilize the oxidant biocides allowing them to suppress the viability of microorganisms over a long time while weakening the negative impact that the oxidant biocides have on the resulting paper and the papermaking equipment. As described in U.S. Pat. Nos. 3,328,294, 3,749,672, 3,170,883, 5,565,109 and 7,651,622 previous attempts at stabilizing oxidant biocides included the use of sulfamic acid, sulfamate stabilized chlorine, monochloramine, DMH stabilized halogen, AmBr—Cl2, and organic nitrogen stabilized chlorine. While somewhat stable, these attempts have proven to be less effective biocides than desired. N-hydrogen sources have also been used to stabilize oxidant biocides but they too have been unsatisfactory because they are volatile and too rigid in their dosage requirements. This rigidity prevents the kind of flexible molar ratio adjustments that are often required to suit the specific conditions of the particular water system they are used to treat. Therefore there is a clear need and utility in an enhanced stabilized halogen biocide which is effective, compatible with other biocides, and flexible in dosage and concentration.
Another technique to address this problem is described in US Published Patent Applications 2006/0231505A and 2003/0029812A1 where they disclose the use of biocide blends. Such blends typically include an oxidant halogen which provides an initial large kill of the organisms and another longer lasting but less effective biocide which provides more long term microorganism suppression. Unfortunately many biocides are themselves incompatible with other biocides and the use of multiple biocides, each having their own preparation and introduction issues, requires an inordinate investment in complex application equipment. Furthermore, multiple biocide feeding machines be installed at various points along a papermaking production line thereby vastly increase the cost and complexity of adding the biocides. So there remains need for simplified making biocide and feeding approach.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.